Thermal printers of the type with which the present invention is concerned are known. They operate with a supply of tape arranged to receive an image and a means for transferring image onto the tape. In one form, a tape holding case or cassette holds a supply of image receiving tape and a supply of an image transfer ribbon, the image receiving tape and transfer ribbon being passed in overlap through a printing zone of the printing device. A printing device operating with a tape holding case of this type is described for example in EP-A-0267890 (Varitronics, Inc.). Other printing devices have been made in which letters are transferred to an image receiving tape by a dry lettering or dry film impression process. In all of these printing devices, the construction of the image receiving tape is substantially the same. That is, it comprises an upper layer for receiving an image which is secured to a releasable backing layer by a layer of adhesive. Once an image or message has been printed on the tape, it is desired to cut off that portion of the tape to enable it to be used as a label. For this purpose, it is necessary to remove the releasable backing layer from the upper layer to enable the upper layer to be secured to a surface by means of the adhesive layer. In EP-A-0267890 scissors are used to cut off the tape.
In another type of printing device described for example in EP-A-0322919 (Brother) a tape holding case holds a supply of image receiving tape, a supply of an image transfer ribbon and a supply of adhesive backing tape. The adhesive backing tape has an adhesive layer for contact with the image receiving tape, a substrate layer and a second adhesive layer covered by a releasable backing layer. The characters are printed onto the image receiving tape, which is transparent, as a mirror image.
In a further printing device, described for example in EP-A-0487313 (Esselte Dymo N.V.), a tape holding case holds a supply of image receiving tape and a supply of image transfer ribbon, the image receiving tape having the same construction as described above with reference to EP-A-0267890. In this device, the cassette includes a feed roller which is rotatably mounted and which cooperates with an output roller of a printing device into which the cassette is inserted to feed the image receiving tape out of the printing device after printing has taken place. After the tape has been fed out of the cassette, the printed portion of the tape is cut off by a cutting mechanism located outside the cassette boundary. A similar arrangement is utilised in EP-A-0322919. EP-B-0364305 describes a cassette which has a portion extending beyond the feed roller to provide an anvil for a cutting blade.
In both of these devices, printing is carried out at a print location defined by a thermal print head and a platen against which the print head presses the image receiving tape and image transfer ribbon during printing. The image receiving tape is then fed past the print location by the feed mechanism comprising the feed roller of the cassette and the output roller of the printing device to a cutting mechanism located outside the cassette boundary. Thus, the distance from the print location to the cutting mechanism can be of the order of 23-25 mm and this defines the blank lead portion of a label. It is desirable to reduce the blank lead portion of a label to avoid wasted blank tape and to improve the appearance of labels. Various methods have been proposed to reduce these leaders, all of which methods have involved the use of software control of the way in which the image receiving tape is printed and fed out. In one aspect, the present invention seeks to provide a reduced length of blank tape on a label without the need for complex software control.
Another disadvantage arising from the printing devices of EP-A-0322919, EP-B-0364305 and EP-A-0487313 is that the tape is cut off using a blade which is brought into contact with the tape while it is supported by an anvil. Not only does the action of a blade against an anvil require a significant amount of cutting force to be applied, but it also results in the wear of cutting blades and a need for their replacement during the life of the printer. Another aspect of the present invention provides a solution to these problems.
Finally, the invention seeks to provide a cassette which can be used in a variety of different types of printing devices.